The general aim of this project is to identify, characterize and study the function of protein factors that regulate vertebrate embryonic development. This is being approached in three ways. One approach is to analyze the expression and regulation of a vertebrate homolog of the Drosophila gene Distal-less. In flies this gene regulates limb and sensory appendage formation. The frog and mouse homologs are expressed in gradients in the limb epithelia, and also in hair follicles and tooth primordia. DNA elements and protein-DNA interactions responsible for this expression pattern are being mapped. This information will be used to test for the function of Distal-less gene expression in frog and transgenic mouse embryos. A second approach employed has been to clone mRNAs encoding protein kinases that are expressed in the early frog embryo. Two such proteins of the receptor tyrosine kinase class, and one cytoplasmic serine- threonine kinase have been isolated and are being studied in frog embryos and in cultured mammalian cells. The third approach focuses on the developmental function of calcium- dependent cell adhesion molecules in the zebrafish neural tube. A novel cadherin, VN-cad, has been cloned, sequenced, and characterized by in situ hybridization. It is being used in "dominant negative" RNA injection experiments to determine its function in zebrafish neurogenesis.